Fire detector



P 13, 1955 P. N. LEHR ET AL 2,717,937

FIRE DETECTOR Filed Oct. 26, 1953 /7 40 22 a 7 7/7 M JZZZ INVENTOR. PHILIP N. LEHR & JOSEF KOCI United States Patent FIRE DETECTOR Philip N. Lehr, Huntington, and Josef Koci, Jackson Heights, N. Y., assignors to Dictograph Products Company, Inc., Jamaica, N. Y., a corporation of Delaware Application October 26, 1953, Serial No. 388,323

7 Claims. (Cl. 200-138) This invention relates to fire detecting apparatus and more particularly to detecting apparatus responsive to a rate of change of temperature exceeding ambient rates as well as to a preestablished maximum temperature.

Fire detecting apparatus which is responsive to rate of change of temperature exceeding ambient changes and also to a preestablished maximum temperature is disclosed in the applicants pending application Ser. No. 230,576, filed June 8, 1951, now Patent No. 2,698,368. That device utilizes a pair of bimetallic elements having different response characteristics and mounted with a thermal conductor strip so that the more sensitive element receives more heat from the fire source. The different rates of deflection cause the elements to touch to complete an electrical circuit to an alarm bell. A slow rise of temperature resulting from normal causes such as the operation of a heating system, will result in a more or less uniform deflection of both elements, under which conditions the elements will not come into engagement and the fire alarm will not be set off. To cause the alarm to be set off after a preestablished maximum temperature is reached, the deflection motion of one element is arrested at a certain point so that the other may catch up with it and close the electrical circuit. The trip point of fire detecting devices of this type tends to be influenced by a relative large number of design factors. Also, false alarms may be set off due to cold rather than heat.

In accordance with the present invention, a simplified and effective fire detecting device for fire alarm systems is provided which responds to a given rate of rise of temperature exceeding preestablished limits and which also responds to a preestablished maximum temperature. A pair of bimetallic elements are mounted in cantilever fashion side by side with one more exposed than the other to possible sources of heat to be detected. The deflecting lengths of both elements are closely controlled by means of a laminated mounting assembly including a common spacer and knife edge member adjustable axially relatively to the elements.

Near the free ends of the bimetallic elements, motion arresting means in the form of insulating abutments is arranged to block the deflecting movement of one element toward the other in response to falling temperatures so that contact between the elements due to cold and the setting off of a false alarm are prevented. This motion arresting action is implemented by making the two elements of different length so that the abutments although effective to arrest movement when the temperature falls, will not interfere with relative movement of the elements when the temperature rises.

For a more complete understanding of the invention, reference may be had to the accompanying drawing in which Figure l is a plan view with the cover removed of a temperature responsive device formed in accordance with the present invention;

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Figure 2 is a view in vertical section taken on the line 22 of Figure 1 looking in the direction of the arrows and showing the cover assembly in place.

Referring to the drawings, the invention is illustrated as embodied in a detecting apparatus comprising a base 11, preferably of electrically insulating material and adapted to be mounted as by screws 12 for example, on a supporting surface such as a wall, bracket or the like. The underside of the base 11 is formed with a recess 13 in which are disposed a pair of terminal or binding posts 14 and 15 by means of which the detector 10 may be connected, for example, in an electrical circuit to an alarm bell (not shown).

The reverse or upper side of the base 11 is formed with raised margins 16 defining a central cavity 16a over which parallel, laterally spaced apart bimetallic elements 17 and 18 are mounted in cantilever fashion by means of a mounting assembly 19. The mounting assembly 19 can be comprised of a shelf 20 surmounted by an insulating spacer 21, one end of the bimetallic element 18, an adjustable wedge-type spacer 22, also of insulating material, one end of the second and outermost bimetallic element 17 and a capping plate 23 of insulating material. The parts of the laminated mounting assembly 19 are held together by means of screws 24 which embrace the elements 17 and 18 and may be tapped into the insulating spacer 21, thereby to clamp the two elements 17 and 18 and the adjustable spacer 22 in place. The spacer 21 is formed with raised and rearwardly extended side portions 21a and 21b which define a channel 210 for receiving the end of the element 13 and the lower portion of the spacer 22. The cap member 23 may also be formed with a channel (not shown) corresponding to the channel 210 to receive the upper element 17 and the upper portion of the spacer 22, thereby to facilitate assembly of the parts as well as adjustment of the two elements and the spacer 22 in directions longitudi nally of the base. The entire assembly may be attached to the base 11 by means of rivets 25 joining the insulating spacer 21 by its side portions 21a and 21b to the base 11.

The lower bimetallic element 18 is longer than the upper bimetallic element 17 and is so positioned in the mounting assembly 19 that it extends beyond the upper element at both ends. The binding post 14 is connected by means of a lug 26 and a conductor 27 to the fixed end of the bimetallic element 17 and the binding post 15 is connected by means of a lug 28 and an electrical conductor 29 to the fixed end of the bimetallic element 18. The free ends of the elements 17 and 18 carry electrical contacts 30 and 31 respectively, and which, when brought together, complete an electrical circuit (not shown) to set off the alarm.

Mounted on the base 11 near the free ends of the bimetallic elements 17 and 18, is an adjustable motion arresting member 32 having a first abutment 33 which overhangs the extended end of the lower bimetallic element 18 and a second abutment 34 which overhangs the relatively shorter end of the bimetallic element 17. The member 32 can be attached for limited adjusting movement to the base 11 by means of a mounting screw 35, thus taking into account tolerances in lengths of the elements 17 and 13. The eiements 17 and 18 are arranged to deflect upwardly with falling temperatures and downwardly with rising temperatures, with the former deflection being arrested by the member 33 to prevent contact between the elements and with the latter deflection being permitted to set off the alarm. The limit of downward deflection of the lower bimetallic element 18 is controlled by an adjustable stop screw 36 threaded into the bottom of the base, in this fashion enabling the upper element 17 to engage the immobilized lower element after a preestablished temperature is reached regardless of the preceding rate of change of temperature. The entire instrument can be encased in a thermal conducting cover 37, the inside surface 37:: of which is blackened opposite the upper surface 17a of the element 17, which is also blackened to facilitate radiant energy transfer.

The adjustable spacer 22 is formed with pairs of clamping edges 22a and 22!) which extend crosswise of and bear tightly against the upper and lower bimetallic elements 17 and 18, respectively. The spacer 22 is adapted to be precisely positioned so as to bring the forward edges 22b and 22a into registration with the forward edges of the insulating spacer 21 and cap member 24 to establish precise deflecting lengths for the elements 17 and 18. To facilitate this adjustment, the parts 21, 22 and 23 are formed with apertures 38, 39 and 40, respectively, which, when aligned with each other and with apertures in the elements 17 and 18, properly position the clamping edges. During adjustment the clamp ing screws 24 are loosened to permit relative axial sliding movement of the spacer 22 and the elements 17 and 18 so that at once the deflecting lengths of the elements and the clamping edges which grip the elements may be readily controlled.

In operation a source of heat such as a hostile fire in the vicinity of the instrument will cause the bimetallic element 17 to deflect downwardly at a faster rate than the inner element 18, this by virtue of its proximity to the cover 37 and the opposed blackened surfaces 17a and 37a, until contact is made between the elements. When the rate of change of temperature is relatively slow as under ambient conditions, elements 17 and 18 will tend to deflect downwardly at more or less the same rate and contact will not occur over a given temperature range. Very high temperatures, however, regardless of the rate at which they are reached, are also indicative of danger and under such conditions it is necessary that the alarm be set off. To this end, the deflection downwardly of the lower bimetallic element 18 is arrested by the adjustable stop 36 so that continuing deflection of the upper element may establish contact to set off the alarm.

In the event the area in which fire is to be detected turns cold the bimetallic elements will tend to deflect upwardly. Ordinarily, this can cause a fire alarm system of this general type to be set off. In the present case, this action is precluded by means of the arresting member 32.

Although a preferred embodiment of the invention has been illustrated and described herein, it will be understood that the invention is not limited thereby but is susceptible to changes in form and detail. Thus the instrument made be made responsive to falling temperatures, rather than rising temperatures by reversing the bimetallic elements. Also, various electrical contact arrangements can be used to vary the control action to meet other requirements. The invention should not, therefore, be regarded as limited except as defined by the following claims.

We claim:

1. In fire alarm apparatus, the combination of a pair of bimetallic thermostat strip elements, means mounting said elements in cantilever fashion in substantially parallel, laterally spaced relationship, one element having its free end extending beyond that of the other, said elements being arranged to deflect in the same direction in response to temperature changes, electrical contact means at the free ends of the elements to be controlled by unequal deflection thereof, and abutment means including a first shoulder overhanging the free end of said one element and interposed in the path of deflection thereof for one direction of movement, and a second shoulder overhanging the free end of said other element and interposed in the path of deflection thereof for one direction of movement, thereby permitting actuation of the contacts following temperature changes in one direction only.

2. Apparatus as set forth in claim 1, including adjusting means to shift said abutment means relatively to said elements.

3. In fire alarm apparatus, the combination of a base portion, a pair of bimetallic thermostat strip elements, means mounting the elements in cantilever fashion in substantially parallel, laterally spaced relationship, a closure for the elements having its inner surface closer to one element than to the other to effect best heat exchange, said one element being slightly shorter than the other at its free end, said elements being arranged so that the one element deflects toward the other and the other deflects away from said one element in response to temperature change to be sensed, electrical contact means at the free ends of the elements to be controlled by unequal deflection thereof, abutment means including a first shoulder overhanging the free end of said other element and interposed in the path of deflection thereof toward the one element, and a second shoulder overhanging the free end of said one element and interposed in the path of deflection thereof toward said closure.

4. Apparatus as set forth in claim 3, including screw means carried by the base portion to shift the abutment means in adjusting movement axially of the said elements.

5. In fire alarm apparatus, the combination of a base portion, a pair of bimetallic thermostat strip elements, means mounting the elements in cantilever fashion in substantially parallel, laterally spaced relationship, a closure for the elements having its inner surface closer to one element than to the other to effect best heat exchange, said one element being slightly shorter than the other at its free end, said elements being arranged so that the one element deflects toward the other and the other deflects away from said one element in response to temperature change to be sensed, electrical contact means at the free ends of the elements to be controlled by unequal deflection thereof, abutment means including a first shoulder overhanging the free end of said other element and interposed in the path of deflection thereof toward the one element, a second shoulder overhanging the free end of said one element and interposed in the path of deflection thereof toward said closure, said electrical contact means comprising a pair of contacts carried at the free ends of the respective elements and adapted to engage following unequal deflection of the elements, and electrical terminal means connected to said elements near their supported ends, said mounting means for the elements affording axial adjustment thereof relatively to the base portion and including a member having a channel for receiving the first element for axial sliding movement, a spacer surmounting the first element and at least partially received in the channel for adjusting movement axially of the elements, the said second element surmounting the spacer, said spacer having upwardly and downwardly facing transverse bearing edges for engaging the first and second elements, respectively, a cap member surmounting the second element, said cap, spacer, first and second elements and base portion having apertures adapted to be brought into alignment to indicate proper proportioning thereof, and clamping means for compressing the said elements across the spacer.

6. In fire alarm apparatus, the combination of a base portion, first and second bimetallic thermostat strip elements, means mounting the elements on the base portion in cantilever fashion in substantially parallel, laterally spaced relationship, said mounting means including a member having a channel for receiving the first element for axial adjustment therein, a spacer surmounting the first element and at least partially received in the channel for axial adjusting movement, said spacer having upwardly and downwardly facing transverse bearing edges, said second element surmounting the spacer, said spacer,

first and second elements and channelled member having apertures adapted to be brought into alignment as indicative of proper mounting positions, and clamping means for compressing the elements across the spacer.

7. In fire alarm apparatus, the combination of a base portion of insulating material, a pair of bimetallic thermostat strip elements mounted in substantially parallel, laterally spaced relationship and adapted to defleet in the same direction in response to temperature changes, a cantilever mounting assembly for the strip elements including a spacer of insulating material between the secured ends of the elements and having transverse bearing edges engaging the respective elements, a pair of plate members of insulating material embracing the elements on opposite sides of the spacer, said members having opposed channels formed therein in alignment with the elements, with the secured end of one element and part of the spacer received in the channel of one member and the secured end of the other element and another part of the spacer received in the opposed channel of the other member, clamping means to compress the respective members, elements and spacer, said members, elements and spacer having apertures formed therein adapted to be brought into alignment to indicate proper positioning, a closure for the element carried by the base portion and having an inside surface closer to one element than the other, the said other element extending outwardly from the mounting assembly for a distance slightly greater than that of the other element and having a back portion extending in the opposite direction from the mounting assembly for a distance greater than the other element, opposed electrical contact means carried by the elements adjacent their free ends, a pair of binding posts carried by the base portion and electrically connected to the respective elements, a first adjustable abutment for limiting the deflection of the longer element toward the base, a second abutment carried by the base and overhanging the respective free ends of the elements to arrest deflecting movement toward the closure, and means to shift the second abutment means in adjusting movement axially with respect to the elements.

References Cited in the file of this patent UNITED STATES PATENTS 2,187,975 Kuhn et a1. Jan. 23, 1940 

